Electric insulator



P. H. THOMAS.

ELECTRIC INSULATOR.

APPLICATION FILED DEC. 17, I917,

1,373,575. Patented Apr. 5, 1921.

um'rco" STATES PATENT omen.

PERCY n. rnomas, or UPPER MONTCLAIR, NEW JERSEY.

ELECTRIC msuna'i'ota.

Specification of Letters Patent.

Patented Apr. 5, 1921.

Original application filed May 16, 1913, Se'rial No. 767,995. Dividedand. this application filed December To all whom it may co /10cm:

Be it, known that I, PERCY H. THoMAs, a citizen of the United States,and resident of Upper Montclair, county of Essex, State of New Jersey,have invented certain new and useful Improvements in ElectricInsulators, of which the following is a specification.

This application is a division of my application Serial No. 767,995filed May 16, 1913, now United States LettersPatent No. 1,250,387,issued December 18, 1917.

My invention relates to insulators for high tension electric lines, suchas power transmission lines. More particularly my insulator is of thesuspension type and is adapted to extra-high tension service.

It is found that the size and cost of high tension insulators, such asare used for high transmission voltages, become excessive as the voltageis raised, and that when several "insulators are used in a string tosupport the line, that the potential of the line is not divided equallybetween them. As a result after a certain number of units have been putin one string little gain is found in adding more units. My inventionprovides an insulator which is relatively. free from these defects andis at the same time cheaper and easier to construct and more convenientin form. I also utilize a novel mechanical principle in insulators ofthis type in that I may rely on vitreous material in tension.

I prefer to use insulating material for the main body of my insulator ofporcelain, glass or other vitreous-material, which has a very highdielectric-quality and is capable of being obtained of great uniformityand high quality. This material has certain mechanical limitations,however, due to manipulation in manufacture so that many desirable formsand methods of construction cannot be used. The insulators here shown,however, are well adapted to the characteristics of the materialsavailable for high'tension insulators.

The ability of any particular insulating device to stand electric strainis known to depend far more on the distribution of the electric stressin the dielectric or insulating material than on the thickness of thedielectric and I- have taken advantage of this principle in myinsulator. I have also used such forms of construction whereby a greaterthickness of insulating material is Serial No. 207,452.

practicable. than in the ordinary insulator constructions.

I also provide a form favorable for resist ng the effects of heavy rainor mist 'whlch tend to cause a breakdown of an insulator. I provide aninsulator that will have a relatively great mechanical strength as wellas good electrical characteristics.

My invention will be understood by reference to the accompanyindrawings, in which F lgure 1 is a sectiona View of a type of semi-rigidsuspension insulator and Fig. 2 1s a cross-section of the insulatorshown in Fig. 1.

Figs. 1 and 2 show a form of insulator where a number of small pieces,extensions, or rods are used arranged to get a better hold on theporcelain than with a single pipe piece, for example and yet formelectrically speaking substantially a single conductor or electrode. Bythis construction thinner porcelain walls than heretofore are obtained,which is an advantage from a manufacturing point of view. This insulatoris shown as made up of two parts, semi-rigidly fastened together. Othernumbers of units than the two shown may be used- The porcelain piecesare shown at 52, the rods used for carrying the load and forming theelectric field are shown at 53 and the metal caps at the top and bottomof the porcelain pieces are shown at 54, 58, 59 and60. The piece 56carries the .piece 54 and the other supporting pieces are fittedtogether mechanically to give strength and to shed the rain as is shown.There are ribs or ridges 55 and 57 on the pieces 56 and 58 which arefilled with cement and serve to v hold the porcelain from breaking outunder strain. Similar means may be used with the other porcelains. Isometimes prefer to extend the center rod 53 to give the effect of asomewhat. rounded terminal at the central portion of theporcelaim'similar to pieces 48, Fig. 6, of the patent referred to togive a somewhat more uniform electric field. This train of insulatorswill swing as a unit and not each unit on the other as may be the casewhen the connection between units isfiexible. The piece 61 carries theline conductor.

I do not limit my invention to the particular construction shown butclaim as well any other embodiment of the same ideas obtainingsubstantially the same results by equivalent means and coming within thescope of the claims.

A part of my invention, therefore, is an insulator adapted to secure arelatively uniform distribution of electric field at the criticalpoints, which will greatly increase the voltage that the insulator willstand,

and to get simple mechanical forms relying in some instances on thetensile strength of porcelain. A suitable distribution of theelectrostatic field in the portion of the main body of the porcelain orother insulating material lying between the metal attachment pieces isimportant, as Well as in the air surrounding the, insulating member,since this will providegreater reliability with a given mi'nimumthiclrness of porcelain, or a -thinner material as may be appropriate.This control of the field Within the porcelain may be attained byproperly shaping the opposing faces of the metallic attachment pieces.For example, as in Figs 1 2, Where there are a plurality of opposingfaces on each attachment piece, the several faces of each attachmentpiece being on a mathematical surface, approximately a plane surface andgenerally parallel the similar surface containing the faces of thesecond attachment pieces.

The distribution of these electrostatic stresses in the porcelain orother insulating material can he made more perfect by making the abovementioned plane surfaces slightly convex toward each other, as shown in"ig". 1 and 2, where the central metallic may be a( vance l slightlyover the outer figures, as described alcove.

I claim:

1. A line insulator including an external attachment and an insulatingmember of vitreous material having three portions, 2:

central portion subjected to the load carried by the insulator andinsulating the metal parts of one end or the insulator from themetal'parts on the other, and two end portions'each rovided With meansfor receiving' and distributing the tension stress from the externalattachment, said means consisting of a group ofmetallic rods insorted inand secured to each end portion,

said groups of rods being symmetrically arranged around a circle thussubmitting the full cross section of the insulating member to asubstantially uniformly distributed mechani al tension stress, togetherwith means for distributing the external mechanical load among the rodsof each group.

2. A line insulator including attachment and an insulating vitreousmaterial having. three member of portions, a

central portion subjected to the tension load carried by the insulatorand insulating the metal parts of one end of the insulator from themetal parts on the other, and two end consisting of a terminal "piecewith a or separated prongs symmetrically afidmr an external israereportions each provided with means for re ceiving and distributingthe'tension stress from the external attachment, said. means consistingof metallic rods inserted in and secured to each end. portion, saidroups of rods being symmetrically arranged with respect to point ofapplication of the force and distributing the stress substantially uni-'portions each provided with means for re-,

ceiving' and distributing the tension stress from the externalattachment, said means consisting of metallic attachment pieces dis-.tributed substantially uniformly through the body of said end portionsand receiving equal portions of the load on the insulator,

*thusproducing the result that no particular portion of the brittlematerial will receive more than its share of the total tensionv stress.

A line insulator including an external attachment and an insulatingmember of vitreous material having three portions, a'

central portion subjected to the tension load "carried by the insulatorand insulating the metal parts of one end of the insulator from themetal parts on the other, and two end portions each provided with meansfor receiving and distributing the tension stress from the externalattachment, sa d means group dividually secured to each end portion ofsaid brittle tension member, all the prongs on one end portion being atone polarity and the prongs on the other end portion at the oppositepolarity.

A line insulator including an external attachment and an insulatingmember of vitreous material having three portions, 3, central portionsubjected to the tension load carried by the insulator and insulatingthe metal parts of one end of the insulator'from the metal parts ontheother, and two end portions each provided with means for receivingand distributing the tension stress from the external attachment, 'saidmeans consisting of groups of thin metal rods colinectcd to terminalpieces and lying parallel to the direction ofthe tension, the rodsconnected to each terminal piece being confined to the end portion ofthe brittle material 1ying adjacent to the said terminal pieces.

6. A line insulator including an external attachment and an insulatingmember of vitreous material having three portions, :1

central portion subjected to the tension load gamma 3 earried by theinsulator and insulating the all electrically and mechanically connectedmetal parts of one end of the insulator from and equ'ally loaded andsymmetrically the metal parts on the other. and two and placed and.attached, one group for each end 10 portions each provided with meansfor reportion.

5 ceiving and distributing the tension stress In iest-imony whereof Ihave signed this from the external attachment, said means specification.'oonsistingof a group of attachment pieces PERGY H. THOMAS.

